In the recording method by means of an inkjet printer which is one of the typical methods among various color recording methods, various methods for discharging ink have been developed. In any of the methods, ink droplets are generated and adhered onto various record-receiving materials (such as paper, film and cloth) to perform recording. This has been rapidly prevailing lately and is expected to continue growing remarkably in the future because of features such as quietness without noise generation due to no contact of a recording head with a record-receiving material and as easiness in downsizing, speeding up and colorizing.
Conventionally, as an ink for fountain pens, felt-tip pens or the like and as an ink for inkjet recording, water-based inks where a water-soluble dye is dissolved in an aqueous medium have been used. In these water-based inks, a water-soluble organic solvent is generally added to prevent ink from clogging at a pen tip or an inkjet nozzle. These conventional inks are required to provide recorded images with sufficient density, not to clog at a pen tip or a nozzle, to dry quickly on a record-receiving material, to bleed less, to be excellent in storage stability, and so on. In addition, the images formed are required to have fastnesses such as water fastness, light fastness and moisture fastness.
Meanwhile, images or character information on color displays of computers are generally expressed by subtractive color mixing of 4 primary color inks of yellow (Y), magenta (M), cyan (C) and black (K) for color recording by an ink jet printer. In order that images expressed by additive color mixing of red (R), green (G) and blue (B) on CRT displays and the like is, as faithfully as possible, reproduced with images expressed by subtractive color mixing, it is desired that each of Y, M and C has a hue as close to each standard color as possible and is also vivid. In addition, it is required that ink compositions to be used for them are stable in storage for a long period of time, and that images printed therewith have a high density and said images are excellent in fastnesses such as water fastness, light fastness and gas fastness.
The application of inkjet printers has been widely spread in the fields ranging from small printers for office automation to large printers for industrial use, and therefore fastnesses such as water fastness, moisture fastness, light fastness and gas fastness have been required more than ever.
Water fastness has been largely improved by coating paper surface with inorganic particulates such as porous silica, cation polymer, aluminasol and special ceramic which can absorb coloring matter in ink, together with a PVA resin and the like.
Moisture fastness means durability against a phenomenon that the coloring matter in a record-receiving material bleeds when the colored record-receiving material is stored under an atmosphere of high humidity. Coloring matter bleeding extremely deteriorates image quality in images particularly required to have a high resolution and photo-like image quality, and therefore it is important to reduce such bleeding as far as possible.
As for light fastness, no technique for large improvement thereof has established yet. In particular, many coloring matters for magenta among 4 primary colors of Y, M, C and K originally have low light fastness, and therefore improvement thereof is an important problem.
In addition, there are more opportunities to print pictures at home with recent spread of digital cameras, and image discoloration by oxidizing gases in the air where printed matters obtained are stored is regarded as a problem. The oxidizing gas reacts with coloring matter on or in recorded paper, causing discoloration or fading of the printed image. Among oxidizing gasses, ozone gas is regarded as a main causative matter accelerating color-fading phenomenon of inkjet-recorded images. This phenomenon of discoloration or fading is characteristic of inkjet images, and therefore improvement of ozone gas fastness is also an important problem.
As a magenta coloring matter used in water-based inks for inkjet recording, typical are xanthene-based coloring matters and azo-based coloring matters using H acid (1-amino-8-hydroxy-naphthalene-3,6-disulfonic acid). Xanthene-based ones are very excellent in hue and vividness but very inferior in light fastness. On the other hand, with respect to azo-based coloring matters using H acid, some are good in terms of hue and water fastness, but many are inferior in light fastness and oxidizing gas resistance such as ozone gas fastness and in vividness. In addition, as for this type, a magenta dye relatively excellent in vividness and light fastness has been developed but it still has a low level in light fastness compared with dyes having a different hue such as a cyan dye represented by a copper phthalocyanine-based coloring matter and a yellow dye.
Examples of a magenta coloring matter excellent in vividness and light fastness include an anthrapyridone-based coloring matter (see, for example, Patent Literatures 1 to 12), but a magenta coloring matter satisfying all the requirements of hue, vividness, light fastness, water fastness, oxidizing gas resistance and solution stability has yet to be obtained.
Patent Literature 1: JP H10-306221 A (pp. 1 to 3 and pp. 7 to 18)
Patent Literature 2: JP 2000-109464 A (pp. 1 to 2 and pp. 8 to 12)
Patent Literature 3: JP 2000-169776 A (pp. 1 to 2 and pp 6 to 9)
Patent Literature 4: JP 2000-191660 A (pp. 1 to 3 and pp. 11 to 14)
Patent Literature 5: JP 2000-256587 A (pp. 1 to 3 and pp. 7 to 18)
Patent Literature 6: JP 2001-72884 A (pp. 1 to 2 and pp. 8 to 11)
Patent Literature 7: JP 2001-139836 A (pp. 1 to 2 and pp. 7 to 12)
Patent Literature 8: WO 2004/104108 A1 Booklet (pp. 20 to 36)
Patent Literature 9: JP 2003-192930 A (pp. 1 to 4 and pp. 15 to 18)
Patent Literature 10: JP 2005-8868 A (pp. 1 to 3 and pp. 15 to 22)
Patent Literature 11: JP 2005-314514 A (pp. 1 to 3 and pp. 15 to 20)
Patent Literature 12: WO 2006/075706 A1 Booklet